Looking through the holder from the end opposite the mirror the direction of the central axis of the holder will appear as a picture of the light emitter. When said picture is placed on the target the firearm has been correctly directed--provided that the sighting device has been mounted properly on the firearm.
Sighting devices of this type--often called "Red Point Devices" because of their red color light emitter--are commonly known and have a number of advantages over traditional sighting devices like e.g. open sighting devices and telescope sights, in which focusing and accommodation is necessary. This makes it possible to shoot more rapidly, both eyes may be kept open, and they facilitate the shooting for persons having weak sight.
Red Point Devices are used at many types of shooting. It may be at extremely rapid shooting at short distances, or it may be at precision shooting at longer distances.
During rapid shooting, the precision demands are often less, and therefore, a somewhat greater and more intensive aimpoint is desired, but at precision shooting the aimpoint should be small and well defined.
The intensity of the surrounding light is also of importance for deciding the intensity of the aimpoint. In dark surroundings the light emitter should be weak, whereas it should be stronger at bright sunlight in order to provide sufficient contrast against the background.
It is desired to have a choice between sighting devices mainly adapted for precision shooting and sighting devices basically for rapid handling of the firearm, i.e. different sizes of the aimpoints.
This has previously been obtained by mounting in front of the light source an aperture defining the size of the aimpoint as recognized by the eye. It has not been possible to use an aperture have variable size, because in the long run movable mechanical parts cannot stand the high acceleration stresses occurring during use of the weapon. Therefore, the problem has been solved practically by using separate sighting devices having different, constant aperture openings for different applications. Thus completely different sighting devices are needed for different types of shooting.